In regard to flushing water tanks for flushing toilet bowls, two types which are provided in a seat type of flush toilet bowl are widely known, i.e., one type where the flushing water tank body is separate from, but secured to, the toilet bowl, and the other being a one piece type where the flushing water tank is integrally formed with the toilet bowl. In these flushing water tanks, the one piece type tank is said to be preferable in terms of the design of the whole toilet bowl, because it can be made lower in height.
In such a flushing water tank, the operation of opening a discharge valve provided to supply flushing water into the bowl of the toilet bowl body is generally carried out by means of a lever provided on the peripheral wall of the tank or a push-button provided on the lid. FIG. 7 shows an example of the construction of operating a discharge valve using a conventional push-button.
This flushing water tank comprises a push-button 53 for operation provided in the middle of the width from side to side of a lid 52 of a tank body 51, and a discharge valve body 54 fitted at the bottom of the tank body 51. The discharge valve body 54 can be brought into and out of a seating engagement with a discharge valve seat 55a which is formed at the lower end of an overflow pipe 55 rising from a discharge opening 51a of the tank body 51, and it is linked to the overflow pipe 55 for up and down swing motion. To the upper end of the overflow pipe 55 is attached an arm 56 by means of a pin 55b, and the arm 56 is linked at one end thereof to the push button 53 and is connected to at the other end to a ball chain 57 connected the discharge valve body 54.
With such a construction, when the push-button 53 is pressed downward, the arm 56 is pivotally moved about the pin 55b clockwise to pull the ball chain 57 upward, thereby allowing the discharge valve body 54 to be opened.
However, in order to pull the discharge valve body 54 upward to a sufficiently high level when the push button 53 is pressed to pivotally move the arm 56, it is necessary to make the length of the arm 56 from the connecting point of the pin 55b to that of the ball chain 57 longer and, accordingly, the length of the arm from the connecting point of the pin 55b to that of the push button 53 becomes shorter. This causes the load which is applied when the push-button 53 is pressed to be concentrated to the upper end of the overflow pipe 55 by way of the pin 55b.
When such a load concentration to the upper end of the overflow pipe 55 occurs, a deflection of the overflow pipe 55 is brought about and the deterioration of the strength thereof is caused by a fatigue due to the repeated load. Such a tendency of the deflection and the deterioration of the strength cannot be ignored since synthetic resin pipes are used for almost all overflow pipes 55.
Also, the lower end portion of the overflow pipe 55 is inserted into the discharge opening 51a of the tank body 51 and is connected to the water supply line of the toilet bowl body being sealed by a sealing means such as a packing or the like. However, if the above-described deflection and the deterioration of the strength occur, the sealed portion is also affected, thus causing the danger of water leakage.
Thus, in the system of operating the discharge valve using the push button, there is a problem of a poor water-sealing property in the discharge valve portion because the push button continues to be pressed longer than the time necessary, thereby causing the concentration of a load applied to the overflow pipe when the operation is carried out.